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Ozawa, Kazumi; Tanigawa, Hiroyasu; Morisada, Yoshiaki*; Fujii, Hidetoshi*
Fusion Engineering and Design, 98-99, p.2054 - 2057, 2015/10
Times Cited Count：1 Percentile：8.47(Nuclear Science & Technology)Reduced activation ferritic/martensitic steel, as typified by F82H, is a promising candidate for structural material of DEMO fusion reactors. To prevent plasma sputtering, tungsten (W) coating was essentially required. This study aims to examine the irradiation effects on hardness and microstructure of vacuum-plasma-spray coated W-F82H steel, with a special emphasis on the impacts of grain-refining induced by frictional stir processing (FSP). It was revealed that the hardness of the VPS-FSP W after ion-irradiation to 5.4 dpa at 800
C were not remarkably changed, where bulk W usually exhibited significant irradiation hardening.
Tanigawa, Hiroyasu; Ozawa, Kazumi; Morisada, Yoshiaki*; Noh, S.*; Fujii, Hidetoshi*
Fusion Engineering and Design, 98-99, p.2080 - 2084, 2015/10
Times Cited Count：14 Percentile：72.58(Nuclear Science & Technology)The vacuum plasma spray (VPS) technique has been investigated as the most practical method to form Tungsten (W) layer as a plasma facing material in fusion devices. The issues are the thermal conductivity and the strength of VPS-W, i.e., the thermal conductivity of VPS-W were significantly lower than that of the bulk W, and the hardness of VPS-W is much less than that of the bulk W. These are mainly caused by the porous structure of VPS-W. In order to solve these issues, friction stir processing (FPS) was applied on VPS-W in this study. It was suggested that FSP can contribute to significant improvement both in mechanical and thermal properties of VPS-W coating.
Nozawa, Takashi; Ozawa, Kazumi; Asakura, Yuki*; Koyama, Akira*; Tanigawa, Hiroyasu
Journal of Nuclear Materials, 455(1-3), p.549 - 553, 2014/12
Times Cited Count：17 Percentile：75.83(Materials Science, Multidisciplinary)SiC/SiC composite is a promising candidate material of fusion DEMO reactor. This paper aims to identify its damage tolerance and strength anisotropy by various characterization techniques such as acoustic emission (AE) monitoring, electrical resistivity (ER) measurement, and digital image correlation (DIC). The AE results identified that damage accumulation initiated prior to the proportional limit stress (PLS) by both tensile and compressive loadings for 2D composites. The preliminary AE waveform analysis implied that this AE detect strength corresponds to initiation of micro-cracking but the stress-strain curve shows further linearity due to the strong interfacial friction. Then fiber sliding occurred near the PLS, followed by the non-linearlity of the curve. The preliminary tensile test results using a notched specimen also suggest notch insensitivity of the composites in any loading directions. The detailed failure mechanism will eventually be discussed with ER and DIC results.
Nozawa, Takashi; Kim, S.*; Ozawa, Kazumi; Tanigawa, Hiroyasu
Fusion Engineering and Design, 89(7-8), p.1723 - 1727, 2014/10
Times Cited Count：13 Percentile：65.04(Nuclear Science & Technology)A SiC/SiC composite is a promising candidate material for the advanced fusion DEMO blanket. For the design of the DEMO, the stability of high-temperature strength of SiC/SiC composites needs to be identified. Additionally, strength anisotropy needs to be clarified because of its unique fabric architecture. This study therefore aims to evaluate mechanical properties by various modes at elevated temperatures, eventually providing a stress envelope for the design. A P/W Tyranno-SA3 fiber reinforced CVI SiC matrix composite with multilayered SiC/PyC interface was evaluated in this study. Tensile and compressive tests were conducted by the SSTT specifically arranged for the high-temperature use. In-plane shear properties were contrarily estimated by the off-axial tensile method assuming that the mixed mode failure criterion is valid for composites. All tests were performed in vacuum. The preliminary test results indicate no degradation of both proportional limit stress (PLS) and the ultimate tensile strength at temperatures below 1000C. Similarly, no significant degradation of high-temperature compressive and in-plane shear properties were identified, finally providing the stress envelope at elevated temperatures for the design.
Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu
Fusion Engineering and Design, 88(9-10), p.2543 - 2546, 2013/10
Times Cited Count：16 Percentile：72.45(Nuclear Science & Technology)A SiC/SiC composite is a promising candidate for a fusion DEMO blanket. Due to the inherent quasi-ductile failure of composites, determining failure scenario for this class of composites is undoubtedly important to develop design codes in practical use of them. This study aims to evaluate the failure behavior of the quasi-ductile SiC/SiC composites to provide a strength map. For this purpose, detailed tensile, compressive and in-plane shear failure behaviors were evaluated by the acoustic emission (AE) technique. The AE results distinguished damage accumulation processes by wavelet analysis. Of particular emphasis is that matrix cracking occurred prior to the PLS by both tensile and compressive loadings because the rough-surface of SiC fibers resulted in the strong frictional stress at the fiber/matrix (F/M) interface. In this paper, an updated failure envelope will be provided by referring the actual matrix cracking stresses as more realistic and reasonable failure criteria.
Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu
Ceramic Materials for Energy Applications II, p.95 - 110, 2012/11
This study aims to identify failure behavior of SiC/SiC composites by varied test modes. For this purpose, acoustic emission (AE) was applied to detect composites' failure. Tensile and compressive tests were conducted for a plain-weave (P/W) chemical vapor infiltration (CVI) composite. Various loading angles were applied to discuss an anisotropic issue. AE results distinguished damage accumulation processes in axial and off-axial loading cases. Specifically, test results indicated a clear difference of damage density between tensile and compressive tests. This study also classified the characteristic failure modes by separately discussing localized variations of power within a time series by wavelet analysis.
Nozawa, Takashi; Ozawa, Kazumi; Choi, Y.-B.*; Koyama, Akira*; Tanigawa, Hiroyasu
Fusion Engineering and Design, 87(5-6), p.803 - 807, 2012/08
Times Cited Count：35 Percentile：90.89(Nuclear Science & Technology)A SiC/SiC composite is a candidate material for a demonstration fusion power reactor. Considering the inherent anisotropy of composites with variety of fabric architecture is required to precisely predict axial and off-axial mechanical properties by various failure modes. This study evaluated crack propagation behavior by the various modes to provide a strength anisotropy map and we discussed a methodology to analytically predict this trend. The strength anisotropy maps identified for various fabric orientations clearly indicate that the composites failed by the mixed modes. Specifically, due to the axial anisotropy, five individual modes such as tensile/compressive strengths in the axial/transverse directions, respectively, as well as the in-plane shear strength, are identified to be essential. In this study, with the analytical criterion based on the Tsai-Wu model, the strength anisotropy could satisfactorily be described.
Matsui, Yoshinori; Takahashi, Hiroyuki; Yamamoto, Masaya; Nakata, Masahito; Yoshitake, Tsunemitsu; Abe, Kazuyuki; Yoshikawa, Katsunori; Iwamatsu, Shigemi; Ishikawa, Kazuyoshi; Kikuchi, Taiji; et al.
JAEA-Technology 2009-072, 144 Pages, 2010/03
JAEA-Technology-2009-072.pdf:45.01MB
"R&D Project on Irradiation Damage Management Technology for Structural Materials of Long-life Nuclear Plant" was carried out from FY2006 in a fund of a trust enterprise of the Ministry of Education, Culture, Sports, Science and Technology. The coupled irradiations or single irradiation by JOYO fast reactor and JRR-3 thermal reactor were performed for about two years. The irradiation specimens are very important materials to establish of "Evaluation of Irradiation Damage Indicator" in this research. For the acquisition of the examination specimens irradiated by the JOYO and JRR-3, we summarized about the overall plan, the work process and the results for the study to utilize these reactors and some facilities of hot laboratory (WASTEF, JMTR-HL, MMF and FMF) of the Oarai Research-and-Development Center and the Nuclear Science Research Institute in the Japan Atomic Energy Agency.
Ozawa, Kazumi; Nozawa, Takashi; Tanigawa, Hiroyasu
no journal, ,
Interfacial properties of unidirectional CVI SiC/SiC minicomposites reinforced with Hi-Nicalon Type-S (HNLS) and Tyranno-SA3 were evaluated. Only HNLS minicomposites with 240- and 1150-nm-thick PyC interphases exhibited a pseudo-ductile behavior. Brittle fracture behavior of other minicomposites was attributed primarily to quite low fiber volume fraction. The HNLS minicomposites with 240-nm-thick exhibited an ultimate tensile strength equivalent to 79-104% of the fiber bundle strength but only 70-85% of the strength of 1150-nm-thick. Based on hysteresis loop analysis, sliding stress estimated for the 240-nm-thick appeared to be about 1.4 times as that for the 1150-nm-thick. This shows that both composites satisfy the GLS condition, but the composite with the thicker interphase could not achieve its fiber bundle strength, probably due to the lower interfacial sliding stress.
Ozawa, Kazumi; Nozawa, Takashi; Tanigawa, Hiroyasu
no journal, ,
A silicon carbide (SiC) matrix composite is a promising candidate for nuclear fusion energy applications. In order to design a damage tolerant composite, fiber/matrix interfacial properties with and without irradiation effects should be thoroughly and systematically understood. For this purpose an approach using model composites is considered to be suitable. This study examines the effects of different fibers and interphases on tensile and interfacial properties of non-irradiated SiC/SiC minicomposites which have high crystalline and near stoichiometric SiC fibers. As a result of the tensile unloading-reloading cyclic tests, following analysis of the hysteresis loops, and the single fiber push-out tests, (1) fiber surface roughness can significantly affect interfacial sliding stress and hence each tensile characteristic such as tensile strength/strain and hysteresis loop width, and (2) interphase thickness would also influence the interfacial and tensile properties.
Ozawa, Kazumi; Koyanagi, Takaaki*; Taguchi, Tomitsugu; Nozawa, Takashi; Tanigawa, Hiroyasu; Kondo, Sosuke*; Hinoki, Tatsuya*
no journal, ,
A SiC/SiC composite is a promising candidate functional/structural material for fusion DEMO reactor. To examine the effects of transmuted H mainly on microstructural cavity formation, the monolithic NITE-SiC with 6wt% Y
O
-AlO sintering additive system were ion-irradiated to 10 dpa at 1000C nominally with 130 appmHe/dpa, and 40 or 400 appmH/dpa, respectively. In SiC grains, tiny cavities with 2 nm formed densely. However, it is revealed that H could not remarkably impact on cavity formation (size, density) in the condition studied. The influence of cavities formed along SiC-YAG grain boundary (GB) on cavity swelling seems to be also small, possibly attributed to its quite low density, even though the cavity size formed is three to five times larger than the size in CVI-SiC matrix in the same irradiation condition. Additional investigation of the microstructural evolution in YAG grain and SiC-YAG GB is a future plan.
Nozawa, Takashi; Nakata, Toshiya; Ozawa, Kazumi; Tanigawa, Hiroyasu
no journal, ,
no abstracts in English
Ozawa, Kazumi; Nozawa, Takashi; Toyoshima, Kazuoki*; Tanigawa, Hiroyasu; Hinoki, Tatsuya*
no journal, ,
no abstracts in English
Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu
no journal, ,
It is being proven that fusion-grade SiC/SiC composites are featured in quasi-ductility with progressive fiber pullouts in fracture, strength anisotropy owing to variety of fabric architecture, notch insensitivity about damage tolerance, edge effect on strength and so on by failure evaluation of this class of composites. From these aspects, a unique materials standards and codes should probably be necessary for composites themselves since they are quite different from ductile metals and brittle ceramics. In this paper, a fundamental concept toward materials codes and standards development specific to the fusion-grade SiC/SiC composites and future actions will be discussed based on the recent achievements.
Ozawa, Kazumi; Nozawa, Takashi; Tanigawa, Hiroyasu; Kato, Yutai*; Snead, L. L.*
no journal, ,
An advanced SiC/SiC composite is a candidate material for fusion DEMO reactor. Four types of model unidirectional SiC/SiC composites (minicomposites) with variations in fiber (Hi-Nicalon Type-S (HNLS), Tyranno-SA3, Sylramic and Sylramic-iBN) by chemical vapor infiltration method were evaluated for tensile and fiber/matrix interfacial properties. The ultimate tensile strength (UTS) increased with the interfacial sliding stress (
) obtained by the hysteresis loop analysis for Tyranno-SA3, Sylramic and Sylramic-iBN. However, this was not the case for the HNLS composite. The composite achieved high UTS due to very low , arising from the larger residual radial tensile stress and smooth fiber surface. In contrast, the fracture behavior of the other composites may have been strongly affected by the clamping stress produced by the relatively rough fiber surfaces.
Tanigawa, Hiroyasu; Ozawa, Kazumi; Morisada, Yoshiaki*; Fujii, Hidetoshi*; Noh, S.*
no journal, ,
no abstracts in English
Nozawa, Takashi; Tanigawa, Hisashi; Hirose, Takanori; Ozawa, Kazumi; Tanigawa, Hiroyasu; Enoeda, Mikio
no journal, ,
A hot isostatic press (HIP) process is a key technology to fabricate a first wall (FW) with cooling channels of the fusion blanket system, and development of the destructive/non-destructive inspection techniques is strongly required. Conventional Charpy impact test is a well-established test method but this technique cannot be applied to the thin-walled cooling channels of the actual component. In contrast, the authors recently proposed a brand new method utilizing a miniature torsion specimen. This study first applied this developmental technique with a miniature specimen to evaluate the HIP joint of the model blanket structure and to evaluate its mechanical properties. The test results show minor difference of the fracture energy but clearly identified that the yield and maximum strength of the HIP joint were equivalent to those of the base metal, eventually identifying the sound structural stability of the HIP joint of the model blanket structure.
Nozawa, Takashi; Ozawa, Kazumi; Tanigawa, Hiroyasu
no journal, ,
A SiC/SiC composite is a candidate material for nuclear fission and fusion applications. Generally, composites failure initiate from inherent internal/surface flaws and hence these flaws as potential failure origins need to be adequately considered in qualification of the material for the practical application. Focusing on the surface flaw issue, identifying notch sensitivity is essential to judge cracking tolerance of composite materials. To date, many extensive work evaluated notch sensitivity of various types of composites and it has almost been concluded that SiC/SiC composites with moderate fiber/matrix interface are notch insensitive by fast fracture monotonically loading mechanical tests. This study aims to further evaluate the notch effects by various failure modes such as cyclic tensile loading/unloading. For that purpose, various damage monitoring methods such as acoustic emission, digital image correlation, etc. are supplementarily adopted.
Nozawa, Takashi; Park, J.-S.*; Nakazato, Naofumi*; Ozawa, Kazumi; Tanigawa, Hiroyasu
no journal, ,
Silicon carbide is a candidate nuclear materials because of low-activation and superior irradiation resistance as well as perceived various characteristics inherently featured as prominent engineering ceramics and a continuous fiber reinforced composite has generally been developed due to brittleness of SiC itself. Of many material parameters for design, validation of high temperature durability at approximately 1000C is essential. Understanding of anisotropy of woven composite strength is also very important. Besides, developing comprehensive model to predict composite strength by various modes with a limited data set. This study aims to summarize the features of fracture behavior by tensile, compressive and shear at elevated temperatures. With consideration of the prediction model, we finally obtain the high temperature strength anisotropy map.
Hamaguchi, Dai; Tanigawa, Hiroyasu; Ozawa, Kazumi; Fujii, Hidetoshi*; Morisada, Yoshiaki*
no journal, ,
Friction-Stir Process were applied to OFCCu in order to evaluate the applicability of the process to mechanically strengthening pure-Cu and possible structural improvement on CuCrZr alloy. In this study, the tool rotational speed was varied from 50 to 500 rpm in order to clarify the effect of rotational speed on the process. The result showed the achievement of very fine grain structure at the rotational speed of 100 and 200 rpm and also the hardness increase to about 1.5 time higher within the stir-zone than that of the base metal at the most. However, the result also revealed that the rapid decrease of the hardness toward a depth direction and relatively shallow stir-zone depth compared to a length of the pin. This can be explained as post-annealing effect due to a good thermal conductivity of a pure-Cu. To avoid the effect, we are considering to introduce compulsory cooling system during the process, which application is more important to a CuCrZr alloy because more rapid cooling and lower thermal diffusion to base metal are required.
